Refractometer, Dipping. A critical angle refractometer which 

 is dipped into the liquid the refractive index of which is to 

 be determined. [14, 26.] 



Refractometer, F6ry. A direct reading refractometer for taking 

 the refractive index for sodium light of oils, solutions and 

 other liquids. [14, 26.] 

 Refractometer, Jamin. A refractometer, for gases or liquids, 



depending on the principle of interference of light. [14.] 

 Refractometer Scale, Leach and Lythgoe's. A slide-rule for use 



in calculations with the refractometer. [19.] 

 Refractor. A refracting telescope. [17.] 

 Refrigerator Thermometer. See Thermometer. [5, 6, 9, 13, 15, 



17, 21, 26, 28.] 

 Regulator. The name given to the standard clock used in 



observations for astronomical work. [15.] 

 Regulator, Arc. The apparatus for maintaining the relative 



distance between the carbons in the electric arc. 

 Reichert Gas Regulator. See Gas Regulator. [2, 4.] 

 Reiset's Apparatus. For the determination of carbon dioxide 



in the atmosphere. 

 Repeating Circle. A reflecting instrument on the principle of 



the sextant, for measuring angular distances, and eliminating 



centreing errors. [2, 10, 13, 15, 27.] 

 Resistance Pyrometer. See Pyrometer. [13, 16.] 

 Resistance Thermometers. See Thermometer. [4, 13, 16.] 

 Resonator. An instrument for facilitating the analysis of 



compound sounds. 

 Respirometer. An instrument for indicating the transpiration of 



a potted plant. 

 Respirometer, Recording. Devised by Prof. Blackman and 



Mr. Paine, for giving a continuous record of the transpiration 



of a potted plant. 



Reticulated Micrometer. See Micrometer. 

 Retinoscope. A form of ophthalmoscope (q.v.) for examining the 



retina. [2, 10, 21, 26.] 

 Revolution-Counter. An instrument for counting the number 



of revolutions of a shaft, etc. See also Trocheameter and 



Variable Speed Recorder. [4, 5, 13, 15, 16. 17, 19, 21, 25, 



26] 

 Revolution-Indicator. An instrument for indicating the number 



of revolutions of an engine, etc. [5, 6, 13, 15, 16, 17.] 

 Revolution-Indicator, Aviation. A revolution counter specially 



devised for indicating the revolution speed of an aeroplane 



propeller. [15.] 

 Rheochord. An instrument consisting of a platinum wire 



mounted on two drums, so that the length of the wire (and 



hence the resistance) included in an electric circuit may be 



varied at will. 

 Rhepgraph, Abraham Projection. A type of oscillograph (q.v.) 



in which the moving systems are formed of small closed 



